Process for producing hydrotalcites and the metal oxides thereof

ABSTRACT

A process for producing high-purity hydrotalcites by reacting alcohols or alcohol mixtures with at least one or more divalent metal(s) and at least one or more trivalent metal(s) and hydrolyzing the resultant alcoholate mixture with water. The corresponding metal oxides can be produced by calcination.

The present invention relates to the production of hydrotalcites.Hydrotalcites are metal hydroxides having a layer lattice and belongingto the group of anionic clay minerals. Furthermore, the presentinvention relates to the metal oxides obtained by calcination of themetal hydroxides produced according to this invention.

Metal hydroxides are important precursors for the production of metaloxides used for instance as raw materials for refractories, ceramics,and supports for heterogeneous catalysts. In nature, metal hydroxidespredominantly occur in the form of mixed metal hydroxides. There arenumerous clay minerals that can be characterised by their layer lattice.The great majority of clay minerals are cationic ones. In said metalhydroxides, cations, e.g. Na⁺, Ca²⁺, etc., are located between thenegatively charged layers. In anionic clay minerals which are far lesscommon, anions are located between the positively charged layers of themetal hydroxide. A large number of said anionic clay minerals arehydroxides of metals of the main group, namely magnesium and aluminium,and hydroxides of transition metals, such as nickel, chromium, zinc,etc. The structure of said clay minerals can be derived from the brucitestructure of magnesium hydroxide Mg(OH)₂. In this structure, some of thedivalent Mg(OH)₆ ⁴⁻ octahedra are replaced by Al(OH)₆ ³⁻ octahedra.Examples of said minerals are meixnerite having the idealised unit cellformula Mg₆Al₂(OH)₁₈.4 H₂O and hydrotalcite (Mg₆Al₂(OH)₁₆CO₃.4 H₂O).According to the prior art, the magnesium : aluminium atomic ratios canbe varied between 1.7 and 4.0. The metal hydroxide octahedra shareadjacent edges to form layers. In addition to water, interstitial anionsrequired for balancing the charge are located between the layers. Theanion nature can be simple, e.g. OH³¹ , CO₃ ²⁻, Cl³¹ or SO₄ ²⁻, orcomplex, as for instance in large, organic or inorganic anions. Up tonow, such anions have been incorporated into the layers by substitutionof simple anions or by acid treatment in the presence of the desiredanions.

Numerous processes for producing stratiform, anionic clay minerals areknown in the art. All of these processes employ metal salts as startingmaterials which are dissolved and then mixed with each other at definedpH-values. See e.g. U.S. Pat. Specification No. 4,539,306 describing theproduction of hydrotalcites for pharmaceutical use, and Reichle, W. T.,Journal of Catalysis, Vol. 94 (1985), p. 547-557, and Nunan, J. G., etal., Inorganic Chemistry, Vol. 28 (1989), p. 3868-3874. Misra et al.have disclosed the production of hydrotalcites having interstitialanions which increase the interlayer spacing by exchanging the anions atelevated temperatures (cf. U.S. Pat. Specification No. 5,075,089).Examples of the incorporation of large, organic anions by anion exchangeare given by Lagaly, G., et al. in Inorganic Chemistry, Vol. 29 (1990),p. 5201-5207. Miyata et al. have described the production ofmagnesium/aluminium hydrotalcites by mixing solutions of the salts MgCl₂and Al₂(SO₄)₃ and a NaOH solution (cf. Clay and Minerals, Vol. 25(1977), p. 14-18). EP-A1-0 536 879 proposes the production ofstratiform, anionic clay minerals by using inorganic anions whichincrease the interlayer spacing, such as B(OH)⁴⁻, V₄O₁₂ ⁴⁻, V₂O₇ ⁴⁻, orHV₂O₇ ³⁻. In said publication, too, solutions of metal salts are mixedat defined pH-values with solutions of the salts that are to beincorporated. Examples of the uses of stratiform, anionic clay mineralsas catalysts are given in U.S. Pat. Specification No. 4,774,212, U.S.Pat. Specification No. 4,843,168, EP-A1-0 536 879, and by Drezdon, M. inACS Symp. Ser., (Novel Mater. Heterog. Catal.), Vol. 437 (1990), p.140-148.

WO-A-93 21 961 describes a process for manufacturing of stratiform,mixed metal hydroxides through controlled hydrolysis of metal oxides ina water free organic solvent with stoichiometric amounts of water. Thethereby obtained metal hydroxides are gel-compositions for use as a dyecarrier in dye laser applications. According to the bottom of page 4this metal hydroxides have the following composition

M_(m)D_(d)T(OH)₄(5−m+d)*nH₂O

wherein M, D, T are monovalent, divalent or trivalent metals, m=0 to 1,d=0 to 1 whereby m+d≠0. The hereby obtained metal hydroxides are nochemical compounds, but gel-like compositions which are unsuitable asprecursors for preparing metal oxides of defined structure according tothe scope of the present invention.

The wide use of stratiform, anionic clay minerals has been impeded up tonow by the fact that for the production starting from metal saltsolutions only a time-consuming, discontinuous synthesis route is known.

Furthermore, catalyst purity is a generally accepted, essentialcriterion. Contaminations caused by alkali—and alkaline earth metals areparticularly undesirable. However, when using metal salts, saidcontaminants cannot be avoided, or they can only be avoided by greatefforts involving high costs. Moreover, there is no process known forproducing clay minerals of the hydrotalcite type with only OH₃₁ -ionslocated in the layers without additional, subsequent ion exchange.

The most important criterion for the catalytic properties of said clayminerals is their basicity. According to the prior art, the basicity issubstantially determined by the Mg:Al ratio. See McKenzie, A. L.,Fishel, C. T., and Davis, R. J. in J. Catal., Vol. 138 (1992), p. 547.Therefore, in order to adjust the catalytic characteristics of acatalyst, it is desirable to provide the widest possible variation ofthe Mg:Al ratio. Furthermore, it has been unknown up to now to producestratiform, anionic clay minerals with a Mg:Al ratio of less than 1.7.

It is the object of the present invention to provide a process forproducing stratiform, anionic clay minerals having the followingadvantages:

time-saving synthesis which can be carried out both continuously anddiscontinuously

use of inexpensive and readily available starting materials

high purities and low alkali concentrations of the stratiform, anionicclay minerals produced by said process

optionally, the possibility of producing stratiform, anionic clayminerals comprising only hydroxide ions as interstitial anions

production of stratiform, anionic clay minerals having sufficientlylarge pore volumes and surface areas required for catalysis

production of stratiform, anionic clay minerals having a Mg:Al ratio ofless than 1.7.

According to the present invention there is provided a process forproducing high-purity hydrotalcites which are stratiform, anionic, mixedmetal hydroxides of the general formula

M_(2x) ²⁺M₂ ³⁺(OH)_(4x+4).A_(2/n) ^(n−).z H₂O

wherein x ranges from 0.5 to 10 in intervals of 0.5, A is aninterstitial anion, n is the charge of said interstitial anion which isup to 8, normally up to 4, and z is an integer of 1 to 6, particularly 2to 4, wherein

(A) metal alcoholate mixtures comprising at least one or more divalentmetal(s), at least one or more trivalent metal(s), and mono-, di-, ortrihydric C₁ to C₄₀ alcoholates are used, said means di- and trihydricmetal alcoholates being substantially used in a molar ratiocorresponding to the stoichiometry of any desired compound according tothe empirical formula referred to hereinabove, and

(B) the resultant alcoholate mixture is hydrolysed with water, the waterfor hydrolysis being used in stoichiometric excess, referring to thereactive valences of the metals used.

The corresponding mixed metal oxide can be produced therefrom bycalcination.

The metal alcoholates can be produced by reacting metals having theoxidation numbers +II or +III with mono-, di- or trihydric C₁ to C₄₀alcohols. The production of the metal alcoholates can be accomplished by

(A) placing the metals jointly into the reaction vessel and then addingthe alcohol, or

(B) producing the metal alcoholates separately, the alcoholatesoptionally having different alcoholate residues, or

(C) consecutively, i.e. by placing one metal into the reaction vessel,adding the alcohol, followed by addition of the second metal, and,optionally, of further amounts of alcohol.

Divalent metals suitable for the production of said alcoholates are Mg,Zn, Cu, Ni, Co, Mn, Ca and/or Fe. Suitable trivalent metals are Al, Fe,Co, Mn, La, Ce and/or Cr.

Prior to or during hydrolysis, any water-soluble, di- or trivalentmetals can be added as metal salts, the metal salts being used insmaller stoichiometric quantities than the metal alcoholates.

The metal alcoholates are produced such that the molar ratio of divalent: trivalent metal alcoholates is from 1:2 to 10:1. They are subsequentlyhydrolysed. Prior to hydrolysis, the alcoholate (alcoholate mixture) maybe filtered to separate any insoluble component.

Suitable alcohols are mono-, di-, and trihydric alcohols having chainlengths of C₁ to C40. They can be branched, unbranched, or cyclic, butbranched and unbranched alcohols with chain lengths of C₄ to C₂₀ arepreferred, and chain lengths of C₆ to C₁₄ are particularly preferred.

For the production of stratiform, anionic clay minerals according tothis invention, the metal alkoxides may be produced from the samealcohols or mixtures of alcohols.

For the production of high-purity clay minerals, the water used forhydrolysis is purified by ion exchange or repeated distillation.Hydroxide anions and/or any other water-soluble anions can be added tothe water for hydrolysis. As organic anions, alcoholate anions areparticularly preferred, but alkyl ether sulfates, aryl ether sulfatesand/or glycol ether sulfates are also suitable; and/or inorganic anionscan be used, particularly carbonate, hydrogen carbonate, nitrate,chloride, sulfate, B(OH)⁴⁻; and/or polyoxometal anions, such as Mo₇O₂₄⁶⁻ or V₁₀O₂₈ ⁶⁻, are also suitable. NH₄ ⁺ is the preferred gegenion. Theanions are incorporated as interstitial anions into the lattices of thestratiform clay minerals formed during hydrolysis, or they areincorporated subsequently by anion exchange as interstitial anions intothe stratiform, anionic clay minerals.

The pH-value of the water for hydrolysis may be in the range of 0 to 14,preferably 1 to 13. The temperature of the water for hydrolysis may befrom 5 to 98° C., preferably 20 to 95° C., most preferably 30 to 90° C.

The hydrotalcites produced according to this invention have interlayerspacings (d-values) of greater than 7 Å, measured on the d(003) reflex.The compositions and physical data of Mg(Zn)/Al clay minerals producedaccording to the invention are listed in Table I.

TABLE I Surf.*^(a) PV*^(a) PR*^(a) CS*^(b) dV*^(b) C.* Al/M²⁺ Formula[m²g] [ml/g] [Å] [Å] [Å] 1 2:1 MgAl₂(OH)₈.4 H₂O 244 0.26 23 7.72 2 1:1Mg₂Al₂(OH)₁₀.4 H₂O 217 0.43 26 210 7.78 3 1:2.5 Mg₅Al₄(OH)₂₂.4 H₂O 2300.13 29 8.22 4 1:1.5 Mg₃Al₂(OH)₁₂.4 H₂O 276 0.78 51 7.82 5 1:2Mg₄Al₂(OH)₁₄.4 H₂O 283 0.69 43 230 7.79 6 1:3 Mg₆Al₂(OH)₁₈.4 H₂O 1900.39 161 7.73 7 1:5 Mg₁₀Al₂(OH)₂₆.4 H₂O 197 0.29 25 8 1:10Mg₂₀Al₂(OH)₄₆.4 H₂O 181 0.35 32 420 9 1:3 Mg₆Al₂(OH)₁₆(NO₃)₂.4 H₂O 1800.32 29 8.73 10 1:3 Mg₆Al₂(OH)₁₆(HCO₃)₂.4 H₂O 190 0.76 174 400 7.79 111:3 Mg₆Al₂(OH)₁₆CO₃.4 H₂O 182 0.77 217 7.77 12 1:3Mg₁₈Al₆(OH)₄₈(Mo₇O₂₄).4 H₂O 26 0.06 22 9.26 13 1:3Mg₆Al₂(OH)₁₆(C₆H₆O₇).4 H₂O 330 0.29 19 11.23 14 1:3Mg₆Al₂(OH)₁₆(C₃H₅O₂)₂.4 H₂O 236 0.57 37 200 13.22 15 1:1.5Mg₃Al₂(OH)₁₀(NO₃)₂.4 H₂O 145 0.24 26 8.98 16 1:1.5 Mg₃Al₂(OH)₁₀(HCO₃)₂.4H₂O 255 1.03 71 7.59 17 1:1.5 Mg₃Al₂(OH)₁₀(CO₃)₂.4 H₂O 268 1.15 101 7.5918 1:1.5 Mg₃Al₂(OH)₈(C₆H₆O₇)₂.4 H₂O 375 0.06 37 am.* 19 1:3Zn₆Al₂(OH)₁₈.4 H₂O 180 0.44 100 am.* Legend: *C = compound a = activatedfor 3 hours at 550° C. Surf. = surface area b = measured on the hydratePV = pore volume PR = pore radius CS = crystallite size dV = d-value am.= amorphous

Metal hydroxides are important precursors for the production of metaloxides. The metal oxides produced according to the invention are used ashigh-purity raw materials for the production of refractories, ceramics,and catalyst supports. The metal hydroxides can be used as highpurity,inorganic ion-exchange materials and mole sieves, as anticariousadditives for tooth pastes, or as antacids, and as additives forplastics, e.g. flame retardants and yellowing inhibitors for PVC.

The stratiform, anionic clay minerals are produced in high purities.This is achieved by the process of the invention which comprisesreacting the metals with alcohols yielding alcoholates, followed bypurification of the alcoholates, e.g. by filtration. Table II gives asurvey of the analytical data of several compounds produced according tothe invention, of the starting metals used and of reference productsobtained by the conversion of metal salts. Reference product A (RP-A)was produced from metal salts, namely reagent-grade nitrate salts, asreported in literature. Reference product B (RP-B) was produced byconversion of metal hydroxides.

TABLE II Analytical Results of Trace Elements Determination by ICP Si FeMn Ti Zn Ga Na Ca Cu Pb Substance [ppm] [ppm] [ppm] [ppm] [ppm] [ppm][ppm] [ppm] [ppm] [ppm] Mg (powder) 64 204 129 <1 13 <5 86  11 10 75 Mg(granules) 46 286 8 3 23 <5 23  9 3 90 Al (needles) 980 2,387   45 36147 98 25  8 22 22 RP-A 303  84 3 2 4 6 890 114 <2 46 RP-B 620 300 11 <111 <5 40 1,650   <2 40 6 50  68 8 <1 15 <5 5  8 <2 <10 3 62  70 15 <1 5<5 6  17 <2 40 1 60  75 19 <2 25 <5 6  11 <2 20 9 58  72 8 1 15 <5 6  204 10

Magnesium powder or granules and aluminium needles (see Table II) wereused for producing the compounds of the invention. The data listed inTable II confirm that the compounds produced according to the inventionhave the desired high purities required for numerous applications. Aparticular advantage is the significantly lower content of alkali—andalkaline earth metals (sodium and calcium) and of silicon and iron allof which have undesirable effects in catalysis.

The X-ray diffraction patterns depictd in FIG. 1 and FIG. 2 are typicalof the compounds produced according to the invention. For comparison,FIG. 3 shows the x-ray diffraction pattern of a compound produced froman aluminium hydroxide/magnesium hydroxide solution. Aluminium hydroxideand magnesium hydroxide are present in unchanged quantities; no clayminerals were formed.

Mixed metal oxides can be produced by calcination of the compoundsproduced according to this invention. For calcination, the compounds ofthe invention were placed into a muffle furnace heated to 550° C.-1,500°C. at which temperatures they were kept for 3 to 24 hours. The mixedmetal oxides thus produced had the same high purities as the mixed metalhydroxides of the invention.

The surface areas of calcined compounds obtained at differentcalcination temperatures are presented in Table III. In order todemonstrate the great surface stability of the compounds producedaccording to the invention in comparison with a product obtained bymixing metal hydroxides, reference product B (RP-B) was calcined underthe same conditions. The metals ratio in reference product B is the sameas in Mg₆Al₂ (OH)₁₈.4H₂O produced according to the invention.

TABLE III Surface Areas of Calcined Compounds Compound/ 3h/ 3h/ 3h/ 3h/3h/ Surface Area [m²/g] 550° C. 750° C. 950° C. 1,200° C. 1,500° C.Mg₆Al₂(OH)₁₈. 190 132 106 33 6 4 H₂O RP-B 138  73  43 32 1

Table IV shows a list of metal hydroxides produced according to theinvention and the metal oxides produced therefrom by calcination.

TABLE IV Metal Oxides from Metal Hydroxide Precursors Compound HydroxidePrecursor Calcined Product 1 MgAl₂(OH)₈ · 4 H₂O MgAl₂O₄ 2 Mg₂Al₂(OH)₁₀ ·4 H₂O Mg₂Al₂O₅ 3 Mg₅Al₄(OH)₂₂ · 4 H₂O Mg₅Al₄O₁₁ 6 Mg₆Al₂(OH)₁₈ · 4 H₂OMg₆Al₂O₉

The x-ray diffraction pattern of a spinel obtained from compound 1 inTable I is depicted in FIG. 4. For comparison, the dashed line shows thex-ray diffraction pattern recorded in the JCPDS file (entry No. 21-1152,MgAl₂O₄, spinel, syn). Thus, it has been proved that a pure-phasespinel, MgAl₂O₄, can be produced by calcining compound 1 according tothis invention.

EXAMPLES General

For the analysis of the compounds produced according to the invention,the metal ratios were determined by inductive plasma spectroscopy. Thecontaminants were determined by the same method. The crystalline phases,crystallite sizes, and d-spacings on the d(001) and d(003) reflexes weredetermined by powder diffractometry. The presence of interstitial ions(OH⁻, HCO₃ ³¹ , NO₃ ³¹ , etc.) was proved by thermogravimetric analysis.The quantity of the water of crystallisation was determined by the samemethod. The quantities found were stated as percent by weight. Thesurface areas and pore radii were determined by the BET method(three-point method), while the pore volumes were determined by mercuryporosimetry. The water content and the quantity of ions located betweenthe layers were determined by thermogravimetric analysis. The compoundsof the invention were calcined in a muffle furnace at temperatures ofbetween 550° C. and 1,500° C.

Example 1

Compound 1 in Table I

Into a 1,000-ml three-neck flask there was placed 15.5 g of aluminiumneedles and 6.5 g of magnesium granules, followed by addition of 239.6 gof hexanol. The mixture was heated. Reaction of the metals with hexanolstarted at approx. 160° C. which was indicated by formation of hydrogenand a temperature increase to approx. 230° C. Then 534.5 g of hexanolwas added to the flask through a dropping funnel. The addition took 60minutes. The reaction mixture was filtered at 90° C. The filtrate wasdivided into three aliquot portions which were hydrolysed in a receiverholding 723.5 g of deionised water containing 0.2 wt. % ammonia. A whiteprecipitate formed immediately. The supernatant alcohol was decanted(optionally, small amounts of alcohol dissolved in the aqueous phase canbe stripped by steam distillation). The resultant slurry was spraydried. The yield was 98% of theoretical. ICP analysis showed analumina/magnesium oxide ratio of 73.2%:26.8% (73%:27%, calculated).Results found by thermogravimetric analysis: residue 50.3% of MgAl₂O₄(49.7% of theoretical), -4H₂O (water of crystallisation) 24.9% (25.2% oftheoretical), -4H₂O 25.4% (25.2% of theoretical).

Example 2

Compound 6 in Table I

Into a 1,000-ml three-neck flask there was placed 7.9 g of aluminiumneedles and 21.1 g of magnesium granules, followed by addition of 122.0g of hexanol. The mixture was heated. Reaction of the metals withhexanol started at approx. 160° C. which was indicated by formation ofhydrogen and a temperature increase to approx. 230° C. Then 574.0 g ofhexanol was added to the flask through a dropping funnel. The additiontook 60 minutes. The reaction mixture was filtered at 90° C. Thefiltrate was divided into three aliquot portions which were hydrolysedin a receiver holding 943.0 g of deionised water containing 0.2 wt. %ammonia. A white precipitate formed immediately. The supernatant alcoholwas decanted (optionally, small amounts of alcohol dissolved in theaqueous phase can be stripped by steam distillation). The resultantslurry was spray dried. The yield was 98% of theoretical. ICP analysisshowed an alumina/magnesium oxide ratio of 32.2%:67.8% (30%:70%,calculated). Results found by thermogravimetric analysis: residue 60.2%of Mg₆Al₂O₉ (59.5% of theoretical), -4H₂O (water of crystallisation)13.2% (12.5% of theoretical), -9H₂O 27.0% (28.0% of theoretical).

Example 3

Compound 9 in Table I

Into a 1,000-ml three-neck flask there was placed 7.9 g of aluminiumneedles and 21.1 g of magnesium granules, followed by addition of 117.0g of hexanol. The mixture was heated. Reaction of the metals withhexanol started at approx. 160° C. which was indicated by formation ofhydrogen and a temperature increase to approx. 230° C. Then 574.0 g ofhexanol was added to the flask through a dropping funnel. The additiontook 60 minutes. The reaction mixture was filtered at 90° C. Thefiltrate was divided into three aliquot portions which were hydrolysedin a receiver holding 876.0 g of deionised water containing 32.2 g ofammonium nitrate. A white precipitate formed immediately. Thesupernatant alcohol was decanted (optionally, small amounts of alcoholdissolved in the aqueous phase can be stripped by steam distillation).The resultant slurry was spray dried. The yield was 98% of theoretical.ICP analysis showed an alumina/magnesium oxide ratio of 30.8%:69.2%(30%:70%, calculated). Results found by thermogravimetric analysis:residue 52.5% of Mg₆Al₂O₉ (51.5% of theoretical), -4H₂O (water ofcrystallisation) 10.6% (10.8% of theoretical), -5H₂O 12.5% (13.5% oftheoretical), -2H₂O -2HNO₃ 24.9% (24.3% of theoretical).

Example 4

Compound 11 in Table I

Into a 1,000-ml three-neck flask there was placed 7.9 g of aluminiumneedles and 21.1 g of magnesium granules, followed by addition of 118.0g of hexanol. The mixture was heated. Reaction of the metals withhexanol started at approx. 160° C. which was indicated by formation ofhydrogen and a temperature increase to approx. 230° C. Then 574.0 g ofhexanol was added to the flask through a dropping funnel. The additiontook 60 minutes. The reaction mixture was filtered at 90° C. Thefiltrate was divided into three aliquot portions which were hydrolysedin a receiver holding 872.0 g of deionised water containing 27.8 g ofammonium carbonate. A white precipitate formed immediately. Thesupernatant alcohol was decanted (optionally, small amounts of alcoholdissolved in the aqueous phase can be stripped by steam distillation).The resultant slurry was spray dried. The yield was 98% of theoretical.ICP analysis showed an alumina/magnesium oxide ratio of 31.8%:68.2%(30%:70%, calculated). Results found by thermogravimetric analysis:residue 56.3% of Mg₆Al₂O₉ (56.9% of theoretical), -4H₂O (water ofcrystallisation) -1H₂O 15.2% (14.9% of theoretical), -6H₂O—H₂CO₃ 28.7%(28.2% of theoretical).

Example 5

Compound 12 in Table I

Into a 1,000-ml three-neck flask there was placed 8.0 g of aluminiumneedles and 21.1 g of magnesium granules, followed by addition of 118.0g of hexanol. The mixture was heated. Reaction of the metals withhexanol started at approx. 160° C. which was indicated by formation ofhydrogen and a temperature increase to approx. 230° C. Then 574.0 g ofhexanol was added to the flask through a dropping funnel. The additiontook 60 minutes. The reaction mixture was filtered at 90° C. Thefiltrate was divided into three aliquot portions which were hydrolysedin a receiver holding 542.0 g of deionised water containing 358.0 g ofammonium molybdate, (NH₄)₆Mo₇O₂₄. A white precipitate formedimmediately. The supernatant alcohol was decanted (optionally, smallamounts of alcohol dissolved in the aqueous phase can be stripped bysteam distillation). The resultant slurry was spray dried. The yield was98% of theoretical. ICP analysis showed an alumina/magnesium oxide ratioof 30.9%:69.1% (30%: 70%, calculated) and a Mo₇O₂₄ content of 42.0%(41.5% of theoretical). Results found by thermogravimetric analysis:residue 82.1% of Mg₁₈Al₆O₂₇ +MO₇O₂₄ (79.0% of theoretical), -12H₂O(water of crystallisation) -24H₂O 21.0% (23.7% of theoretical).

Example 6

Compound 17 in Table I

Into a 1,000-ml three-neck flask there was placed 11.3 g of aluminiumneedles and 15.1 g of magnesium granules, followed by addition of 176.0g of hexanol. The mixture was heated. Reaction of the metals withhexanol started at approx. 160° C. which was indicated by formation ofhydrogen and a temperature increase to approx. 230° C. Then 456.0 g ofhexanol was added to the flask through a dropping funnel. The additiontook 60 minutes. The reaction mixture was filtered at 90° C. Thefiltrate was divided into three aliquot portions which were hydrolysedin a receiver holding 782.0 g of deionised water containing 39.8 g ofammonium carbonate. A white precipitate formed immediately. Thesupernatant alcohol was decanted (optionally, small amounts of alcoholdissolved in the aqueous phase can be stripped by steam distillation).The resultant slurry was spray dried. The yield was 98% of theoretical.ICP analysis showed an alumina/magnesium oxide ratio of 49.0%:51.0%(46%:54%, calculated). Results found by thermogravimetric analysis:residue 53.0% of Mg₃Al₂O₆ (52.0% of theoretical), -4H₂O (water ofcrystallisation) -H₂O 19.9% (21.0% of theoretical), -3H₂O—H₂CO₃ 25.1%(27.1% of theoretical).

Example 7

Compound 18 in Table I

Into a 1,000-ml three-neck flask there was placed 11.3 g of aluminiumneedles and 15.1 g of magnesium granules, followed by addition of 176.0g of hexanol. The mixture was heated. Reaction of the metals withhexanol started at approx. 160° C. which was indicated by formation ofhydrogen and a temperature increase to approx. 230° C. Then 456.0 g ofhexanol was added to the flask through a dropping funnel. The additiontook 60 minutes. The reaction mixture was filtered at 90° C. Thefiltrate was divided into three aliquot portions which were hydrolysedin a receiver holding 729.0 g of deionised water containing 92.7 g ofammonium citrate, (NH₄)₂C₆H₆O₇. A white precipitate formed immediately.The supernatant alcohol was decanted (optionally, small amounts ofalcohol dissolved in the aqueous phase can be stripped by steamdistillation). The resultant slurry was spray dried. The yield was 98%of theoretical. ICP analysis showed an alumina/magnesium oxide ratio of49.7%:50.3% (46%: 54%, calculated). Results found by thermogravimetricanalysis: residue 42.9% of Mg₃Al₂O₆ (39.9% of theoretical), -4H₂O (waterof crystallisation) 13.4% (12.9% of theoretical), -4H₂O—C₆H₈O₇ 42.9%(38.7% of theoretical).

Example 8

Compound 6 in Table I, but Separate Preparation of the Metal Alcoholates

Into a 500-ml three-neck flask there was placed 7.9 g of aluminiumneedles, followed by addition of 50.0 g of hexanol. The mixture washeated. Reaction of the metal with hexanol started at approx. 160° C.which was indicated by formation of hydrogen and a temperature increaseto approx. 230° C. Then 220.0 g of hexanol was added to the flaskthrough a dropping funnel. The addition took 60 minutes. The reactionmixture was filtered at 90° C. Into a 500-ml three-neck flask there wasplaced 21.1 g of magnesium granules, followed by addition of 120.0 g ofhexanol. The mixture was heated. Reaction of the metal with hexanolstarted at approx. 150° C. which was indicated by formation of hydrogenand a temperature increase to approx. 200° C. Then 307.0 g of hexanolwas added to the flask through a dropping funnel. The addition took 60minutes. The reaction mixture was filtered at 90° C. The two alcoholateswere combined. The quantity obtained was divided into three aliquotportions which were hydrolysed in a receiver holding 943.0 g ofdeionised water containing 0.2 wt. % ammonia. A white precipitate formedimmediately. The supernatant alcohol was decanted (optionally, smallamounts of alcohol dissolved in the aqueous phase can be stripped bysteam distillation). The resultant slurry was spray dried. The yield was98% of theoretical. ICP analysis showed an alumina/magnesium oxide ratioof 32.1%:67.9% (30%:70%, calculated). Results found by thermogravimetricanalysis: residue 60.1% of Mg₆Al₂O₉ (59.5% of theoretical), -4H₂O (waterof crystallisation) 13.3% (12.5% of theoretical), -9H₂O 26.9% (28.0% oftheoretical).

Example 9

Compound 6 in Table I, but use of Mixed Alcohols

Into a 1,000-ml three-neck flask there was placed 7.9 g of aluminiumneedles and 21.1 g of magnesium granules, followed by addition of 120.0g of a mixture of butanol, hexanol, and octanol (1:7:2). The mixture washeated. Reaction of the metals with the alcohol mixture started atapprox. 150° C. which was indicated by formation of hydrogen and atemperature increase to approx. 210° C. Then 552.0 g of the alcoholmixture was added to the flask through a dropping funnel. The additiontook 60 minutes. The reaction mixture was filtered at 90° C. Thefiltrate was divided into three aliquot portions which were hydrolysedin a receiver holding 900.0 g of deionised water containing 0.2 wt.%ammonia. A white precipitate formed immediately. The supernatant alcoholwas decanted. Butanol and small amounts of hexanol and octanol dissolvedin the aqueous phase were stripped by steam distillation. The resultantslurry was spray dried. The yield was 97% of theoretical. ICP analysisshowed an alumina/magnesium oxide ratio of 32.2%:67.8% (30%: 70%,calculated). Results found by thermogravimetric analysis: residue 60.4%of Mg₆Al₂O₉ (59.5% of theoretical), -4H₂O (water of crystallisation)13.0% (12.5% of theoretical), -9H₂O 27.1% (28.0% of theoretical).

Example 10

Compound 19 in Table I Conversion of a Metal Alcoholate and a Metal PlusAlcohol

Into a 1,000-ml three-neck flask there was placed 7.9 g of aluminiumneedles, followed by addition of 50.0 g of hexanol. The mixture washeated. Reaction of the metal with the alcohol started at approx. 160°C. which was indicated by formation of hydrogen and a temperatureincrease to approx. 230° C. Then 220.0 g of hexanol was added to theflask through a dropping funnel. The addition took 60 minutes. Then115.3 g of zinc diethanolate was added. The mixture was allowed to coolto 90° C. prior to filtration. The filtrate was divided into threealiquot portions which were hydrolysed in a receiver holding 510.0 g ofdeionised water containing 0.2 wt. % ammonia. A white precipitate formedimmediately. The supernatant alcohol was decanted (optionally, smallamounts of the alcohol dissolved in the aqueous phase can be stripped bysteam distillation). The resultant slurry was spray dried. The yield was96% of theoretical. ICP analysis showed an alumina/zinc oxide ratio of16.8%:83.2% (17%:83%, calculated). Results found by thermogravimetricanalysis: residue 72.2% of Zng₆Al₂O₉ (71.6% of theoretical), -4H₂O(water of crystallisation) 9.1% (8.7% of theoretical), -9H₂O 19.5%(19.7% of theoretical).

What is claimed is:
 1. A process for producing high purity hydrotalciteswhich are stratiform, anionic mixed metal hydroxides of the generalformula M_(2x) ²⁺ M₂ ³⁺(OH)_(4x+4).A_(2/n) ^(n−).zH₂O wherein M_(2x) ²⁺,M₂ ³⁺ are divalent and trivalent metal(s) respectively, x ranges from0.5 to 10 in intervals of 0.5, A is an interstitial anion selected fromthe group consisting of a hydroxide anion and an organic anion, n is thecharge of said interstitial anion, and z is an integer of 1 to 6,comprising (A) mixing at least one divalent metal alcoholate with atleast one trivalent metal alcoholate, both metal alcoholates being metalalcoholates of mono-, di-, or trihydric C1 to C40 alcoholates, wheresaid mono-, di- and trihydric metal alcoholates being mixed in a molarratio corresponding to the stoichiometry of the formula referred tohereinabove, and (B) hydrolyzing the resultant alcoholate mixture withwater, the water for hydrolysis being used in stoichiometric excess,referring to the reactive valences of the metals used and where thesource of the interstitial anions for A is from the water-soluble anionscontained in the water for hydrolysis.
 2. A process for producing metaloxides by calcinating the hydrotalcites produced according to claim 1.3. A process according to claim 1 wherein the metal alcoholates arefirst produced by reacting metals having the oxidation numbers +II or+III with the alcohols according to claim 1, the production of saidmetal alcoholates being accomplished by a process element selected fromthe group consisting of (A) placing the metals jointly into the reactionvessel and then adding the alcohol, (B) producing the metal alcoholatesseparately, the alcoholates having same or different alcoholateresidues, and (C) consecutively, by placing one metal into the reactionvessel, adding the alcohol, followed by addition of the second metal. 4.A process according to claim 1 wherein the divalent metals used areselected from the group consisting of Mg, Zn, Cu, Ni, Co, Mn, Ca and Feand the trivalent metals used are selected from the group consisting ofAl, Fe, Co, Mn, La, Ce and Cr.
 5. A process according to claim 1wherein, prior to or during the hydrolysis, as a third or additionalmetal component, water-soluble, di- and/or trivalent metals as metalsalts are added, the metal salts being used in molar quantities smallerthan the metal alcoholates, and the total molar ratio of the divalent:trivalent metals being as defined in claim
 1. 6. A process according toclaim 1 wherein for the hydrolysis, water is used which containswater-soluble anions selected from the group consisting of: a. hydroxideanions; and b. organic anions selected from the group consisting ofalcoholates alkyl ether sulfates aryl ether sulfates and glycol ethersulfates.
 7. A process according to claim 1 wherein prior to hydrolysisthe metal alcoholate mixture is filtered.
 8. The process of claim 3where in process element (C) further amounts of alcohol are added afterthe addition of the second metal.
 9. The process of claim 6 where theorganic anions are selected from the group consisting of alcoholates,alkyl ether sulfates, aryl ether sulfates, and glycol ether sulfates.10. The process of claim 6 where the counterion is ammonium and theanion is hydroxide ion.
 11. A process for producing high purityhydrotalcites which are stratiform, anionic mixed metal hydroxides ofthe general formula M_(2x) ²⁺M₂ ³⁺(OH)_(4x+4).A_(2/n) ^(n−).zH₂O whereinM_(2x) ²⁺, M₂ ³⁺ are divalent and trivalent metal(s) respectively, xranges from 0.5 to 10 in intervals of 0.5, A is an interstitial anionselected from the group consisting of a hydroxide anion and an organicanion, n is the charge of said interstitial anion, and z is an integerof 1 to 6, comprising (A) mixing at least one divalent metal alcoholatewhere the metal is selected from the group consisting of Mg, Zn, Cu, Ni,Co, Mn, Ca and Fe, with at least one trivalent metal alcoholate wherethe metal is selected from the group consisting of Al, Fe, Co, Mn, La,Ce and Cr, and both metal alcoholates being metal alcoholates of mono-,di-, or trihydric C1 to C40 alcoholates, where said mono-, di- andtrihydric metal alcoholates being mixed in a molar ratio correspondingto the stoichiometry of the formula referred to hereinabove, and (B)hydrolyzing the resultant alcoholate mixture with water, the water forhydrolysis being used in stoichiometric excess, referring to thereactive valences of the metals used, and where the hydrolysis waterused contains water-soluble, organic or inorganic anions and where thesource of the interstitial anions for A is from the water-soluble anionscontained in the water for hydrolysis.
 12. A process for producing metaloxides by calcinating the hydrotalcites produced according to claim 11.13. The process according to claim 11 wherein the metal alcoholates arefirst produced by reacting metals having the oxidation numbers +II or+III with the alcohols according to claim 11, the production of saidmetal alcoholates being accomplished by a process element selected fromthe group consisting of (A) placing the metals jointly into the reactionvessel and then adding the alcohol, (B) producing the metal alcoholatesseparately, the alcoholates having same or different alcoholateresidues, and (C) consecutively, by placing one metal into the reactionvessel, adding the alcohol, followed by addition of the second metal.14. The process according to claim 11 wherein, prior to or during thehydrolysis, as a third or additional metal component, water-soluble, di-and/or trivalent metals as metal salts are added, the metal salts beingused in molar quantities smaller than the metal alcoholates, and thetotal molar ratio of the divalent: trivalent metals being as defined inclaim
 1. 15. The process according to claim 11 wherein for thehydrolysis water contains water-soluble anions selected from the groupconsisting of: a. hydroxide anions; and b. organic anions selected fromthe group consisting of alcoholates, alkyl ether sulfates, aryl ethersulfates, and glycol ether sulfates.
 16. A process for producing highpurity hydrotalcites which are stratiform, anionic mixed metalhydroxides of the general formula M_(2x) ²⁺M₂ ³⁺(OH)_(4x+4). A_(2/n)^(n−).zH₂O wherein M_(2x) ²⁺, M₂ ³⁺ are divalent and trivalent metal(s)respectively, x ranges from 0.5 to 10 in intervals of 0.5, A is aninterstitial anion selected from the group consisting of a hydroxideanion and an organic anion, n is the charge of said interstitial anion,and z is an integer of 1 to 6, comprising (A) mixing at least onedivalent metal alcoholate with at least one trivalent metal alcoholate,both metal alcoholates being metal alcoholates of and mono-, di-, ortrihydric C1 to C40 alcoholates, where said mono-, di- and trihydricmetal alcoholates being mixed in a molar ratio corresponding to thestoichiometry of the formula referred to hereinabove, and where theproduction of said metal alcoholates being accomplished by a processelement selected from the group consisting of (i) placing the metalsjointly into the reaction vessel and then adding the alcohol, (ii)producing the metal alcoholates separately, the alcoholates having sameor different alcoholate residues, and (iii) consecutively, by placingone metal into the reaction vessel, adding the alcohol, followed byaddition of the second metal (B) filtering the metal alcoholate mixture,(C) hydrolyzing the resultant alcoholate mixture with water, the waterfor hydrolysis being used in stoichiometric excess, referring to thereactive valences of the metals used and where the source of theinterstitial anions for A is from the water-soluble anions contained inthe water for hydrolysis.
 17. The process according to claim 16 whereinthe divalent metals used are selected from the group consisting of Mg,Zn, Cu, Ni, Co, Mn, Ca and Fe and the trivalent metals used are selectedfrom the group consisting of Al, Fe, Co, Mn, La, Ce and Cr.
 18. Theprocess according to claim 16 wherein for the hydrolysis water containswater-soluble anions selected from the group consisting of: a. hydroxideanions; and b. organic anions selected from the group consisting ofalcoholates, alkyl ether sulfates, aryl ether sulfates, and glycol ethersulfates.